1. Field of the Invention
The invention relates, generally, to antikinin compounds, and specifically to uses of the pentapeptide, Arg-Pro-Pro-Gly-Phe (RPPGF)(SEQ ID NO:1). More specifically, the invention relates to the use of RPPGF (SEQ ID NO:1) to screen for an RPPGF (SEQ ID NO:1) receptor and for antagonists and mimetics of RPPGF. The invention also relates to the use of RPPGF (SEQ ID NO:1) to treat diseases.
2. Background Art
All animal life regulates the internal biological environment via hormonal systems. These often consist of gene product-protein substrates synthesized in depots (such as the liver, or specific endocrine organs), and highly specific proteolytic enzymes called either proteases or proteinases, which attack specific peptide bonds in the substrates to cleave out smaller, generally very potent peptide hormones of various length and sequence. After these peptide hormones bind to their specific receptors, usually expressed upon the surface of target cells in target tissues, and induce signal transduction to ultimately cause some biological response, the hormones are metabolized by enzymes called peptidases, which are more generally non-specific and, thus, capable of cleaving multiple peptide hormones to smaller, generally inactive peptide fragments.
Two, unusually interlocking, substrate-protease-peptide hormone-peptidase systems are the renin-angiotensin system. The protein antigotensinogen (also called renin substrate) is made in the liver, attacked in the blood by the specific protease called renin, synthesized, stored and released from the kidney, to cleave out angiotensin I, a decapeptide with surprisingly little biological activity. However, after removal of its' C-terminal histidine, leucine by a second enzyme called angiotensin I-converting enzyme (ACE), which is enriched on the surface of pulmonary vascular endothelial cells, the octapeptide angiotensin II is formed, an extremely potent vasoconstrictor and, thus, a regulator of vascular resistance (blood pressure) and other physiologic processes.
More than twenty years ago, the first potent synthetic inhibitors of angiotensin I-converting enzyme, based upon an unusual, natural pentapeptide inhibitor of the enzyme found in the venom of the South American viper, Bothrops jararaca, were reported (1). These inhibitors (the so-called, "ACE" inhibitors), are now amongst the world's most widely used antihypertensive drugs.
From the outset of work on the natural (or subsequent synthetic) inhibitors of ACE (angiotensin converting enzyme), it was known that this enzyme is bifunctional, that is, it has two natural substrates, and in fact, its' preferred substrate is not angiotensin I, but rather the deca- or nonapeptide hormones called lysyl-bradykinin (kallidin) or bradykinin (2). For this reason, the same enzyme is also called kininase II (there are several other peptidases for kinins including a kininase I). However, rather than forming an active hormone in this role, ACE/kininase II catabolizes the kinins by sequentially removing two dipeptides from the C-terminal end to fragments which have uniformly been considered to be inactive degradation products of the kinin peptides (2). Because the kinin peptides are amongst the most powerful vasodilator (hypotensive) peptides known, there is increasing consideration of the possible roles of kinins in blood pressure control (3). In addition, and finally there are recent discoveries suggesting that fragments of some peptide hormones, widely considered to be inactive, are capable of producing biological responses (4-6).
Bradykinin (BK) is the cleavage product of the action of the enzyme tissue kallikrein upon the substrate, low molecular weight kininogen. The plasma half-life of the generated BK is short (.sup..dagger. 1/2.about.15 secs.). The degradation of BK is the result of proteolytic cleavages produced by the enzymes kininase II (ACE) and other peptidases such as kininase I and neutral endopeptidase 24.11. The initial digestion of BK by kininase II results in the removal of the terminal phenylalanine-arginine, leaving the heptapeptide des-Arg9-Phe8-BK. Subsequent cleavage of des-Arg9-Phe8-BK results in additional BK fragmented peptides, including the pentapeptide BK1-5. These degradation peptides of BK, including BK1-5, have been considered for decades to be inactive.
The generation and degradation of BK occurs during episodes of tissue damage, allergic reactions and inflammatory responses. BK has been shown to mediate the body's responses to these events. BK's principal cardiovascular effect is one of vasodilation. In fact, BK has been shown to be a mediator in the pathological hypotension associated with septic (endotoxin) shock. Conversely, prolongation of the half-life of BK by ACE inhibitors may contribute to the beneficial actions of these drugs (3). Thus, BK is now considered to be important to cardiovascular responsiveness to homeostatic perturbations.
There is no prior art considering the possibility that kinin fragments have any counter regulatory influence to modulate the actions of the parent kinins.
Determining if endogenous metabolites of BK have any previously undetected role in homeostatic responses to perturbations or disease would allow for the development of stable mimetics of this metabolite as therapeutic agents. Development of such mimetics would be useful for treatment of pathological conditions in which BK has been shown to be detrimental, such as endotoxin shock.
The present invention provides the surprising discovery that RPPGF (SEQ ID NO:1) has many pharmacologic activities that are opposed to the activity of bradykinin.